The invention relates to a magnetic radial bearing having electromagnets which are arranged distributed in the circumferential direction. Bearings of this type are also referred to as active magnetic bearings or active magnet bearings. The invention also relates to a magnetic bearing system which has a magnetic radial bearing of the aforementioned type as well as a three-phase controller for rotating field excitation and a DC supply for the magnetic bias excitation. The three-phase controller is preferably a converter.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
To ensure clarity, it is necessary to establish the definition of several important terms and expressions that will be used throughout this disclosure. The term “radial” refers to a direction toward and away from a rotation axis of the supported rotor shaft. The term “axial” refers to a direction parallel to the rotation axis. The term “in the circumferential direction” refers to tangential directions around the rotation axis of the rotor shaft. When the bearing for the rotor shaft is in use, the rotation axis of the rotor shaft actually corresponds to a structural rotation axis and to a rotational axis of symmetry of the magnetic radial bearing.
Conventional magnetic radial bearings have been previously disclosed which include six-electromagnets which are offset by 60° in the circumferential direction, thus representing a rotating-field machine stator with a three-phase winding. At least one additional coil is provided to produce the magnetic bias. The electromagnets are connected in star or delta to a three-phase controller.
Bearings of this type are intended for a non-contact, wear-free bearing of a rotor shaft of a rotating machine. The machines under consideration may have a mass of more than one ton and an electrical rating of more than 500 kW, or even several Megawatts. Machines of this type are, for example, electric motors, generators, turbomachines, compressors, pumps and the like. They may have a maximum rotation speed of 4000 rpm or more. During use, an air gap preferably in the range from 0.3 mm to 0.5 mm is maintained between the magnetic radial bearing and the supported rotor shaft.
It would therefore be desirable and advantageous to provide an improved magnetic radial bearing, which obviates prior art shortcomings and specifically has an otherwise comparable bearing characteristics and a simpler winding design. It would also be desirable to provide a magnetic bearing system with a magnetic radial bearing of this type.